The research described in this proposal will explore the physical organization and a possible function of the repeated sequences found in most eucaryotic DNA. Bovine and Drosophila DNA will be sheared to known size, denatured, partially renatured, and the resulting hybrids visualized in the electron microscope. Analysis of the these hybrids will determine the size distribution and the linear organization of the repetitive DNA. The possibility of using T4 gene 32 protein and anti-DNA antibodies to differentiate double stranded from single stranded DNA in the electron microscope will be explored. Autoradiography of copy RNA transcribed from isolated middle repetitive DNA and hybridized insitu to Drosophila polytene chromosomes will be performed to learn about the gross organization of these sequences. Heterochromatin from Samoaia leonensis which probably contains DNA of a single simple sequence will be isolated and the proteins included in this chromatin characterized by polyacrylamide gel electrophoresis. In addition, the repeating base sequence of the satellite DNA from this fly will be determined.